1. Field of the Invention
The present invention relates to composite vibrators, vibration gyros using the vibrators, and electronic apparatuses incorporating the gyroscopes. In addition, the invention relates to methods of manufacturing the composite vibrators. More particularly, the invention relates to composite vibrators incorporated in video cameras with a shake preventing function, car navigation systems, pointing devices, or the like, vibration gyroscopes using the vibrators, electronic apparatuses incorporating the vibration gyroscopes, and methods of manufacturing the composite vibrators.
2. Description of the Related Art
FIG. 22 shows a perspective view of a conventional vibration gyroscope. In this figure, a vibration gyroscope 60 includes a tuning bar vibrator 600 and a frame 610. The turning bar vibrator 600 includes a first piezoelectric member 101 polarized in its thickness direction, with a first electrode 104a and a second electrode 104b having the same dimensions being formed on a main surface thereof, a second piezoelectric member 102 polarized in its thickness direction, with a third electrode 105 formed on a main surface thereof, and conductive support members 106a, 106b, 106c, and 106d. The first electrode 104a and the second electrode 104b are arranged in the longitudinal direction of the tuning bar vibrator 600 at a predetermined distance in the width direction. The other main surface of the first piezoelectric member 101 is bonded to the other main surface of the second piezoelectric member 102 via an intermediate electrode 103. In each of the first and second piezoelectric members 101 and 102, a ratio between the length L1 of the thickness direction and the length L2 of the width direction, that is, the value of L1/L2 is set to be approximately 1. In the tuning bar vibrator 600, in positions (near nodes N1 and N2) in which the nodes N1 and N2 (axes) of bending vibrations at both free ends in the thickness direction are projected perpendicularly to a main surface of the tuning bar vibrator 600, the support member 106a is connected to the first electrode 104a, the support member 106b is connected to the second electrode 104b, and the support members 106c and 106d are connected to the third electrode 105. The frame 610 is made of resin and has a sufficiently large mass. The end portions of the support members 106a, 106b, 106c, and 106d are fixed to the frame 610.
The vibration gyroscope 60 having the above structure performs bending vibrations at both free ends when an excitation signal is applied to the third electrode 105 via the support members 106c and 106d. The nodes obtained in the vibrations are N1 and N2 as axes orienting in the width direction of the vibration gyroscope 60. When there is applied an angular velocity whose rotational axis is the longitudinal direction of the tuning bar vibrator 600, the vibration gyroscope 60 performs bending vibrations at both free ends in the width direction orthogonal to the direction of excitation. The vibration nodes obtained in this case are N3 and N4 as axes orienting in the thickness direction substantially at the center in the width direction of the vibration gyroscope 60. Signals of bending in the width direction are output from the first electrode 104a and the second electrode 104b. 
In the vibration gyroscope 60, when the tuning bar vibrator 600 vibrates in the thickness direction and the width direction, the center of gravity shifts. Then, the vibrations of the tuning bar vibrator 600 partially leak to the outside frame 610 via the support members 106a, 106b, 106c, and 106d. The frame 610 absorbs the vibrations leaking from the tuning bar vibrator 600.
Conventional vibration gyroscopes are described in Japanese Unexamined Patent Application Publication No. 7-332988, and the like.
In general, a vibrator gyroscope requires miniaturization. Particularly, the length of the longitudinal direction of a tuning bar vibrator needs to be reduced, since the length is longer than the lengths of the widthwise and thickness directions thereof. However, the sensitivity of a vibration gyroscope is proportional to a given angular velocity, a vibration velocity of a vibrator, and the mass of the vibrator. Thus, when the length of the longitudinal direction of the tuning bar vibrator is reduced, the mass of the composite vibrator decreases and thereby the sensitivity of the vibration gyroscope is deteriorated.
In addition, when the vibrations of the tuning bar vibrator leaks outside, the amplitude of the vibrator is attenuated. As a result, the sensitivity of the vibration gyroscope is deteriorated.
In addition, due to the deteriorated sensitivity of the vibration gyroscope, the ratio of noise with respect to signal increases. Furthermore, since the temperature characteristics of support members and an acceleration detecting circuit become more influential, a value detected for an angular velocity tends to change.
Accordingly, it is an object of the present invention to provide a composite vibrator which can maintain high sensitivity even when miniaturized.
In addition, it is another object of the invention to provide a method of easily manufacturing the composite vibrator.
In addition, it is another object of the invention to provide a vibration gyroscope using the composite vibrator, which can maintain high sensitivity even when miniaturized.
In addition, it is another object of the invention to provide an electronic apparatus using the vibration gyroscope capable of accurately detecting an angular velocity to precisely control the angular velocity.
To this end, according to the present invention, there is provided a composite vibrator including a plurality of tuning bar vibrators having the same length and support members for supporting the tuning bar vibrators. In this composite vibrator, the tuning bar vibrators with both ends free are arranged in a direction orthogonal to a longitudinal direction of the tuning bar vibrators and are coupled with each other in the vicinity of nodes of bending vibrations.
In addition, the plurality of tuning bar vibrators may include at least two tuning bar vibrators having the same configuration.
In addition, each tuning bar vibrator may include an electrode to which a signal for exciting the tuning bar vibrator is applied and an electrode from which a signal corresponding to bending vibration of the tuning bar vibrator in a direction orthogonal to the direction of excitation is output.
In addition, adjacent tuning bar vibrators may be excited in mutually opposite directions.
In addition, a resonant frequency in the exciting direction of at least one of the tuning bar vibrators may coincide with a resonant frequency in the direction orthogonal to the exciting direction.
In addition, at least two electrodes formed in the longitudinal direction of a main surface of each tuning bar vibrator may be arranged at a predetermined distance in the width direction thereof.
According to the present invention, there is provided a vibration gyroscope including a driving unit for driving the composite vibrator and a detecting unit for detecting an angular velocity via the composite vibrator.
Further there is provided an electronic apparatus including the above vibration gyroscope.
There is provided a method of manufacturing a composite vibrator. The method includes a first step of bonding an auxiliary substrate to a second main surface of a base substrate, a second step of completely cutting the base substrate from the direction of a first main-surface side of the base substrate while leaving a part of the auxiliary substrate to form a plurality of tuning bar vibrators arranged in a width direction, the relative positions of the tuning bar vibrators being retained by the auxiliary substrate, a third step of bonding support members to the first main surfaces of the tuning bar vibrators, and a fourth step of separating the auxiliary substrate from the second main surfaces of the tuning bar vibrators.
In addition, the base substrate may have electrodes formed on both main surfaces thereof.
In addition, the base substrate may be formed by bonding two piezoelectric substrates polarized in mutually opposite directions with respect to the thickness direction thereof.
Alternatively, the base substrate may be formed by bonding a conductive substrate to a piezoelectric substrate polarized in the thickness direction.
In addition, the second step may include forming grooves along one of the longitudinal and width directions on the first main surfaces of the tuning bar vibrators.
In addition, the third step may include bonding the support members in the vicinity of nodes of bending vibrations of the tuning bar vibrators with both ends free.
In addition, the composite vibrator manufacturing method may further include a fifth step of bonding support members to the nodes on the second main surfaces of the tuning bar vibrators after the first to fourth steps are performed.
In the above arrangement of the composite vibrator of the invention, since the plurality of tuning bar vibrators is coupled with each other, the mass of the composite vibrator increases. Thus, even when the length of the longitudinal direction is reduced, due to the increased mass, its sensitivity for the detection of an angular velocity is improved.
Additionally, in the composite vibrator of the invention, since the tuning bar vibrators are excited in mutually opposite directions to be bent in mutually opposite directions, the vibrations of the tuning bar vibrators are trapped inside and thereby the vibrations hardly leak outside. As a result, since loss caused by the leaked vibrations of the tuning bar vibrators decreases, the angular-velocity detection sensitivity is improved.
In addition, since the vibration gyroscope of the invention uses the composite vibrator with high detection sensitivity, its angular-velocity detection sensitivity is improved.
In addition, since the vibration gyroscope of the invention uses the compact composite vibrator, miniaturization of the vibration gyroscope can be achieved.
Furthermore, in the method of manufacturing the composite vibrator according to the invention, in the first step, the base substrate is bonded to the auxiliary substrate, and while keeping the bonding state, the second and third steps are sequentially performed. Thus, without causing positional deviation of the tuning bar vibrators, the composite vibrator including the tuning bar vibrators having the same configuration can be easily manufactured.
Furthermore, the electronic apparatus of the invention uses the vibration gyroscope capable of accurately detecting an angular velocity with high sensitivity, a precise controlling mechanism can be formed.